The present invention relates to ear protective devices, i.e., earplugs. More specifically, the invention concerns earplugs of the fluid expansible variety, wherein an earplug element once inserted into the ear can be expanded to obtain a form-fitting seal.
Over the years, a variety of constructions have been proposed for earplugs designed to protect against hearing loss due to excessive noise, and/or to seal off the ear canal and thereby protect the ear from the entry of water, dust, or other potentially harmful matter. A well known class of earplug relies on the deflection of soft rubber flanges, cones, bulbs or like elements to plug the ear canal and hold the plug in place. See, e.g., Watson et al. U.S. Pat. No. 2,437,490; Knudsen U.S. Pat. No. 2,246,736; and Ochi et al. U.S. Pat. No. 4,540,063. These types of devices cause pressure points within the ear which can eventually, if not immediately, cause irritation to the user.
In another variety, the earplug consists of a segment of soft foamed plastic material which the user squeezes down to a small diameter and inserts quickly into the ear canal, allowing the foam to expand within the ear canal. See, e.g., Leight U.S. Pat. No. 4,434,794 and Gardner, Jr. U.S. Reissue Pat. No. 29,487. This type of earplug is more comfortable, but is difficult to insert into the ear and often does not retain well. The insertion of this type of earplug into the ear can be likened to pushing on a rope and usually cannot be performed quickly enough before significant expansion has occurred. Moreover, foamed plastic plugs inherently have many pores which trap contaminants and are subject to bacterial growth. As a result, for hygienic reasons, it is generally recommended that foamed plastic earplugs be discarded after only a couple of uses.
Attempts have also been made to construct form-fitting earplugs using resiliently expansible chambers filled/tillable with a fluid such as a gas or a liquid, or a viscous material such as a paste, gel or putty.
In Mills U.S. Pat. No. 3,736,929, a dumbbell shaped elastic envelope contains a viscous filler such as a soft wax, gel, plastic or silicone putty. Two cavities are connected by a restricted passageway ("commissure"). The plug is inserted into the ear by squeezing down one cavity (and simultaneously expanding the other cavity) and inserting the squeezed down cavity into the ear canal. The elasticity of the envelope thereafter causes the filler material to flow back into the squeezed down cavity so that the outer wall thereof expands into sealing contact with the ear canal. With this design, the expansion force of the inserted cavity against the ear canal is fixed by the characteristics of the filler material and the envelope. Since independent control of the expansion degree by the user is not possible, the result may be an expansion force insufficient to create a good seal, or an excessive expansion force resulting in user discomfort. Moreover, given the criticality of the flow characteristics of the filler material, the design does not allow for use of relatively inexpensive liquid or gaseous fillers.
Wasserman U.S. Pat. No. 2,876,767 discloses an earplug having a resilient bladder that is inflatable with air once inserted into the ear. A one-way valve assembly incorporated into each earplug, and a separate syringe, are required to accomplish the inflation. A valve arrangement is also provided for allowing air to escape from the bladder. In addition to its obvious structural complexity, this design would be difficult to use, e.g., due to the required manipulation of a separate filling tool (syringe) before each use.
Akiyama U.S. Pat. No. 4,060,080 discloses an earplug with a pair of resilient fluid-filled chambers. Once an insertion end of the plug is inserted into the ear canal, a fluid contained in a first chamber at an opposite end of the plug is squeezed into a second chamber at the insertion end, whereby the insertion end is expanded. Catch means are provided for maintaining the first chamber in a collapsed condition so that the second chamber remains inflated. With this arrangement, the degree of filling of the second chamber is not adjustable to suit the individual user--the first chamber must always be collapsed to the same position. An uncomfortable fit or inadequate seal may thus result.
Michael et al. U.S. Pat. No. 2,824,558 likewise discloses an earplug having a pair of resilient fluid chambers, wherein once an insertion end of the plug is inserted into the ear canal, a fluid contained in a storage chamber at an opposite end of the plug is squeezed into a second chamber at the insertion end. Rather than employing a catch in order to maintain the first chamber in a collapsed condition, the Michael et al plug utilizes a resilient one-way check valve that opens responsive to increased pressure generated in the storage chamber upon squeezing the same, then closes to maintain the second chamber in an expanded condition. While advantageously allowing a user to adjust the degree of filling of the second chamber, the design suffers from a disadvantage in that the valve arrangement is relatively complex. It also requires a preliminary pressure release step when it is desired to remove the earplug.
An additional limitation of all of the valved earplugs discussed above is their unidirectional nature, i.e., the plugs all have a specific insertion end. Since the plug can be inserted from one end only, manipulation of the plug into the single proper insertion orientation is required before insertion.